How does technique and technique modification impact on knee loads in sporting tasks?

[Truncated abstract] Anterior cruciate ligament (ACL) rupture is a serious and debilitating injury that usually results in an athlete undergoing reconstructive surgery and remaining out of sport for an extended period. Therefore the incidence of this injury although only moderate (approximately one per professional Australian football team per year) when considered from a social and sporting cost perspectives is of serious concern. However, the non-contact nature of the majority of occurrences of this injury indicates that it may be possible to reduce the incidence with interventions aimed at modifying the movement and/or physical characteristics of individual athletes. Previous research aimed at reducing the risk of non-contact ACL injury has focused on improving support of general knee loads, particularly valgus and internal rotation moments, which are known to load the ACL, during sporting tasks through the utilisation of balance and plyometric training. While technique cues have been included in a number of these training programs there has been no research that has investigated training to change isolated aspects of sidestep cutting and landing techniques and their effect on valgus and internal rotation moments at the knee, the moments thought to cause non-contact ACL injury. This was the overarching theme of this thesis. Most non-contact ACL injuries occur during either sidestep cutting or landing tasks, as such, the relationship between technique and knee loads was investigated within these two tasks. The first study presented in this thesis investigated how performing sidestep cuts with various extreme postures affected knee moments. ... The technique modification aimed at bringing athletes' torsos upright and forward facing, based upon the results of the previous studies. It also aimed to increase knee flexion angle, as this is still the current literature recommendation. Post-intervention participants displayed an increase in maximal knee flexion angles but no change in torso positioning. This kinematic change was correlated to a significant increase in peak internal rotation moments, with no change in valgus or flexion moments. Although, due to the angle at which the peak internal rotation moment occurred it was identified that this increase in moment may not increase the risk of non-contact ACL injury risk, due to the increased potential for muscular support and decreased transmission of the moment to the ACL. However, it was concluded that the technique modification program may not be appropriate for reducing the risk of non-contact ACL injury, within the particular landing task chosen. Overall this thesis identified that whole body kinematics are related to knee moments during sidestep cutting and landing. Kinematics associated with increase valgus and internal rotation moments at the knee tended to reflect joint posture observed during actual non-contact ACL injuries. Secondly a six week technique modification program is capable of modifying both sidestep cutting and landing technique. Technique changes result in changed knee moments. However, the complex nature of the relationship between technique and knee loads indicates that any potential intervention aimed at reducing the risk of non-contact ACL injury, should be tested in the laboratory utilising tools such as neuromuscular modelling and stochastic modelling to ensure the planned intervention has the potential to be successful prior to implementing the protocol in an epidemiological testing scenario.